1. Field of the Invention
The present invention generally relates to a fuel cell such as a solid oxide fuel cell or the like which has an electrolyte, a fuel electrode and an air electrode, and which generates electric energy by electrochemical reaction, and more particularly to a fuel cell having a following feature: a combustion heater is incorporated in the fuel cell, thereby improving both the starting performance and restarting performance of the fuel cell.
2. Description of the Related Art
A fuel cell has a structure where a high-performance electrolyte for conducting an ion such as an oxygen ion (O2−), a proton (H+) or the like is held between a porous air electrode and a porous fuel electrode. Moreover, the fuel cell generates an electromotive force by respectively supplying oxidizing gas containing oxygen gas to the air electrode side and reducing gas containing hydrogen or hydrocarbon gas to the fuel electrode side, and electrochemically reacting these gases with each other through the electrolyte.
As a conventional solid oxide fuel cell (Hereinafter, Solid Oxide Fuel Cell is abbreviated to SOFC.) which is a type of such fuel cells, for example, Japanese Patent Application Laid-Open No. H5-205753 discloses an SOFC including a flat-plate stack formed by alternately laminating single cell plates and separators, each single cell plates having an anode and a cathode respectively arranged on a front surface and a backside of a solid electrolyte plate, and each separator having a gas groove formed on one side to distribute fuel gas, and a gas groove on the other to distribute oxidant gas. Further, Japanese Patent Application Laid-Open No. H8-102327 discloses a hollow flat-plate fuel cell plate for forming a cell plate including a plurality of gas passages inside and also a separator function.
Generally, in such an SOFC, an operating temperature reaches 800 to 1000° C., so that heating must be carried out up to the operating temperature at starting time of the fuel cell. However, in the above publications, no mention is made of specific means for heating such a fuel cell stack.
Meanwhile, with regard to a cylindrical stack, a paper “A 1000-cell SOFC reactor for domestic cogeneration”, pp. 271 to 274 of Journal of Power Sources 71 (1998), describes power generation by introducing fuel to cylindrical inner sides of a plurality of cylindrical cells, and air to outsides of the cells. In addition, the paper describes a process of introducing a mixture of hydrogen and air to the inside of the cell cylinder at starting time, and igniting it for combustion by an ignition coil arranged on an upper side of cell.
Also, an article “Concept and technology of DH-Q-SOFC for efficient use of fossil fuel resources in electric vehicles” presented at 45th SOFC workshop (held on May 9, 2001) describes installation of a combustion cylinder separately from a cell.